The invention relates to a cylinder-piston unit for a needle-free injector, with a chamber which is arranged in a cylinder and is intended for receiving an injection solution, an end wall with at least one nozzle bore or an outlet element, and pistons arranged movably in the chamber. The invention furthermore relates to a method for correspondingly filling the cylinder-piston unit.
Cylinder-piston units are inserted into injectors which are known, for example, from US 2008/014997 A1, DE 10 2007 004 211 A1 or DE 10 2007 008 369 A1.
Liquid drugs are understood by injection solution. The specialized terms used will be explained in more detail below. The term drugs is known to a person skilled in the art. These include substances or mixtures of substances for human or animal medicine. They comprise the pharmaceutical active compound or active compounds and further customary components rendering said active compound pharmaceutically usable, in particular water.
DE 10 2005 054 600 A1 discloses a cylinder-piston unit with a cylinder and a piston which is guided therein, wherein the cylinder and the piston enclose a chamber which is at least temporarily fillable with active compound, and the cylinder has at least one outlet element at its front end. The cross section of the chamber or the cross section of the inner wall of the cylinder increases at least in areas from the front to the rear. At least in the front region—which faces the outlet element—the piston has a front, elastic skirt, the front outer edge of which, when the piston is unloaded, spans a cross-sectional area which is larger than an area spanned by a contour lying in the region of the transition from the skirt to the skirt-bearing piston section.
DE 10 2006 040 888 B3 discloses a closure system for containers for storing or administering liquid, pasty or powdery substances, said closure system comprising a cap provided with a passage hole, and a closure element. In this case, the cap holds the closure element in a frictional and/or form-fitting manner on the container in the region of the opening to be closed by means of a latching element present on the container. The end surface which surrounds the container opening and on which the closure element rests has a depression. The closure element is a virus-proof, bacteria-proof and spore-proof film which lies on the end surface and, at least in areas, over the depression. When the cap is placed on, an elastomer or adhesive ring which fills the depression is arranged between the closure element and the depression.
DE 10 2006 045 959 B3 discloses a cylinder-piston unit with a cylinder and a piston which is guided therein and is sealed by rubber in a sterile manner, wherein the cylinder and the piston enclose a chamber which is at least temporarily fillable with active compound, and the front end of the cylinder has at least one outlet element. The piston which is at rest in a rear position is sealed in a sterile manner in relation to the cylinder by a static rear sealing element, wherein, in a sealing position, the two sealing elements bear in each case on the cylinder wall and on the piston wall. A parking space receiving the respective sealing element is arranged spatially behind each static sealing element. When the piston is actuated, the individual static sealing elements are transferred from their respective sealing position into a parking position located in the parking space, wherein, in the parking position, each sealing element makes contact either only with the cylinder wall or only with the piston wall. At least one dynamic sealing element which is on the piston side and, at least when the piston is actuated, bears against the inner wall of the cylinder is arranged between the two static sealing elements.
In the known embodiments, the cylinder-piston unit is filled with the injection solution either directly prior to use by the user of the disposable injector or the injection solution is placed into the cylinder-piston unit at the manufacturing factory and it is then also stored in the cylinder-piston unit. A finished injection solution is therefore present in the cylinder-piston unit for the duration of the possible storage time. One possible, preferred manner of storing an active compound involves freeze-drying (lyophilizing) the active compound solution and storing the active compound in the form of a powder. A lyophilizate of this type has a longer shelf life than in dissolved form. In order to obtain a finished injection solution prior to the injection, the lyophilized active compound is dissolved in a solvent, such as water. An injectable solution is subsequently present.
Proceeding from said prior art, the invention is based on the object of specifying a cylinder-piston unit for receiving an injection solution and a method for filling the cylinder-piston unit, in which the injection solution is produced from a first drug component and a second drug component and is mixed to be ready or is dissolved only shortly prior to use. The further task is to design a cylinder-piston unit into which an injection solution which is to be freeze-dried can be placed in a sterile manner, said solution can then be freeze-dried and subsequently closed in an airtight and sterile manner. The solvent for the lyophilizate has to be stored adjacent thereto in such a manner that, in the event of use, said solvent can dissolve the lyophilizate to form an injection solution ready for use. Prior to application, said solution has to be located in a manner free from gas bubbles in a cylinder which is temporarily stable at up to 300 bar and has a nozzle which is to be released in a sterile manner and from which said solution can be shot under high pressure and without a needle through the skin into, for example, the subcutaneous fatty tissue.